Retorting of oil shale with special heat carriers

ABSTRACT

1. IN A METHOD FOR RETORTING CRUSHED OIL SHALE CONTAINING CARBONACEOUS ORGANIC MATTER AND MINERAL MATTER WHEREIN OIL SHALE IS RETORTED BY CONTACTING SAID OIL SHALE WITH PARTICULATE HOT HEAT CARRIERS IN A RETORT ZONE TO GAS AND OIL PRODUCTS, PARTICULATE SPENT SHALE, AND AN ORGANIC COMBUSTIBLE DEPOSITION ON AT LEAST A PORTION OF SAID HEAT CARRIERS, SAID HEAT CARRIERS HAVING BEEN HEATED IN A DEPOSITION BURNING ZONE TO A RETORT ZONE INLET TEMPERATURE OF BETWEEN 1000*F. AND 1400*F. MAINLY BY COMBUSTION OF A COMBUSTIBLE CARBON-CONTAINING DEPOSITION ON SAID HEAT CARRIERS, SAID HEAT CARRIERS BEING IN AN AMOUNT SUFFICIENT TO PROVIDE AT LEAST 50 PERCENT OF THE HEAT REQUIRED TO VAPORIZE A MAJOR PORTION OF THE CARBONACEOUS MATTER FROM SAID OIL SHALE AND TO HEAT SAID CRUSHED OIL SHALE FROM ITS RETORT ZONE INLET TEMPERATURE TO A RETORT ZONE OUTLET TEMPERATURE OF BETWEEN 800*F. AND 1150*F, ABD WHEREIN SAID GAS AND OIL PRODUCTS ARE SEPARATED AND RECOVERED, THE IMPROVEMENT WHEREIN SAID HEAT CARRIERS ARE COMPRISED OF PARTICULATES HEAT BODIES AND PELLETS IN A SIZE RNGE BETWEEN ABOUT 0.005 INCH AND 0.05 INCH, SAID HEAT BODIES HAVING A LOW SURFACE AREA LESS THAN 0.1 SQUARE METER PER GRAM OF SAID HEAT BODIES, SAID PELLETS HAVING A RELATIVELY HIGH SURFACE AREA AT LEAST AS GREAT AS 20 SQUARE METERS PER GRAM OF SAID PELLETS SAID HEAT CARRIERS CONTAINING BETWEEN 10 AND 90 PERCENT BY WEIGHT OF SAID HEAT BODIES AND BETWEEN 90 AND 10 PERCENT BY WEIGHT OF SAID PELLETS, AND COMBINED AVERAGE SURFACE AREA OF SAID HEAT BODIES AND SAID PELLETS IN SAID HEAT CARRIERS BEING BETWEEN 10 AND 150 SQUARE METERS PER GRAM.

Oct. 15, 1974 D. K. WUNDERLICH ET AL 3,841,993

RETORTING OF OIL SHALE WITH SPECIAL HEAT CARRIERS Filed on. 26. 1973 zSheets-Sheet 1 FLUE GAS PELlaET V DEP smow BURNING. I; COMBUSTION GASZONE PRIMARILY I5 GAS AND OIL HOT SPECIAL VAPORS HEAT CARRIERS Y 2225 129 w RETORT 43 u ZONE sEPARAT|0N HEAT CARRIER PRIMARILY LIFTING l HEATCARRIERS FIG. I

Oct. 15, 1974 WUNDERUCH EI'AL 3,841,993

RETORTING OF OIL SHALE WITH SPECIAL HEAT CARRIERS 2 a n a 9 h 5 2 S 2 s.u. 9 a II I w m a Q 7 S VHA f i L a w fifi flxm 2 2 E wwl W DOD. t DOD.I r" 3 3 7. A m. m 4 l I 9 U 3 3 4 l q. A a 5 Filed 001;. 26. 1973United States Patent 3,841,993 RETORTING OF OIL SHALE WITH SPECIAL HEATCARRIERS Donald K. Wunderlich and James L. Skinner, Richardson, Tex.,assignors to Atlantic Richfield Company, Los Angeles, Calif.

Continuation-impart of application Ser. No. 287,669, Sept. 11, 1972,which is a continuation-in-part of apphcatlon Ser. No. 284,288, Aug. 29,1972, both now abandoned. This application Oct. 26, 1973, Ser. No.409,957

Int. Cl. Cb 53/06 U.S. Cl. 208-11 Claims ABSTRACT OF THE DISCLOSURE Hotspecial solid heat carriers comprised of a mixture of low internalsurface area heat bodies and relatively high internal surface areapellets are cycled to a retort zone to retort crushed oil shale therebyproducing gas and oil products, particulate spent shale, and acombustible deposition on the pellets. The combustible deposition on thepellets provides the main source of heat for heating the heat carriersthereby increasing the utility of the carbon-containing residue normallyformed during retorting. The pellets carry sensible heat to the retortzone, improve the quality of the liquid products, and collect thecombustible deposition. The low surface area heat bodies carry sensibleheat, coact with the pellets to regulate the etfective surface area andquantity of the heat carriers relative to the oil shale, and providegreater operating flexibility to the retorting process. In an oil shaleprocessing operation, the overall result is an increase in liquid oilyield. After retorting, the heat carriers are separated from at least 95percent by Weight of the spent shale smaller than the heat carriers. Theheat carriers are then passed or lifted to a combustion zone Where thecombustible deposition on the pellets is burned to reheat the heatcarriers.

CROSS-REFERENCES TO RELATED APPLICATIONS This application is acontinuation-in-part of copendiug application Ser. No. 287,669, filedSept 11, 1972, entitled Retorting Oil Shale with Special Heat Carriers,now abandoned, which was a continuation-in-part of copending applicationSer. No. 284,288, filed Aug. 28, 1972, now abandoned, entitled RetortingOil Shale with Special Pellets, by the same inventors as thisapplication and owned by a common assignee.

BACKGROUND OF THE INVENTION This invention relates to a process forretorting of the solid carbonaceous organic matter in crushed oil shale.In this process, special heat carriers comprised of low internal surfacearea heat bodies and relatively high internal surface area pellets arecycled through a retorting system.

As a preliminary stage in the production of petroleum oils and gases,the solid carbonaceous organic solid matter or kerogen in oil shale ispyrolyzed or retorted. The term retorting denotes thermal con-version ofkerogen or organic matter to oil vapors and gas thereby leavingparticulate spent shale and includes separation of the oil vapors andgas from the spent shale. The spent shale contains residual carbonaceousorganic matter and matrix mineral matter. In an overall commercialoperation, the products or yield of retorting are processed inadditional stages, for example, solids separation, condensation,fractionation, coking, hydrogenation, and the like, depending on thetypes of marketable products being produced.

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Frequently, the yields of various processes are compared with FischerAssay yields. For a description of the Fischer Assay refer to Method ofAssaying Oil Shale by a Modified Fischer Retort by K. E. Stanfield andI. C. Frost, R. I. 4477, June 1949, U.S. Department of Interior.

When the kerogen is retorted, a normally gaseous fraction, a normallyliquefiable vaporous fraction, and an organic residue are formed. Theproduct distribution between gas, liquid, and residue is indicative ofthe distribution of the various boiling point-fractions in the liquidproduct. It is highly desirable to obtain a liquid product that isdirectly adaptable to prerefining and avoids or lessens the amount ofresidue or 975 F. plus fraction that must be subjected to coking orother similar treatments. In many retorting processes control over theproduct distribution is virtually absent, and in others, any attempt toreduce the need for coking and the like by altering the boiling pointdistribution in the liquids either results in too much unusablematerial, or too much gas product, or too much organic residue or 975 F.plus fraction, or any combination thereof, which in turn e ventuallyresult in a loss of liquid oil yield. Any advantage obtained byattempting to control product or residue conversion is frequently olfsetby undesirable shifts in other process variables or results. Inaddition, the kerogen content of the oil shale inherently or naturallyfluctuates between rich and lean and many processes are not sufiicientlyflexible to control product distribution when the kerogen contactvaries.

Some advances to more flexible and efficient control over the productsof retorting and of other process variables have been made by usingsolid heat-carrying bodies which exhibit good heat transfer propertiesand supply the heat needed for retorting with a reduction in processproblems. In such processes, the heat-carrying bodies and the oil shalefeedstock are intermixed thereby retorting oil vapors and gases from thefeedstock. The heat-carrying bodies are usually heated in a separateheating zone by burning combustible fuel material, such as heavy residor natural gas. But in general, this method of heating necessitatesadditional equipment and creates additional handling problems.

Others have proposed cycling the spent shale and supplying some of theheat by burning the residual carbonaceous organic matter or solidorganic char developed in the retort zone, or cycling catalyst particlesand supplying some of the heat by burning carbon deposited on thecatalyst (for example, U.S. Pat. 3,281,349). In this latter process, thesurface area of the catalyst particles is not specified. Some types ofcatalyst particles frequently have high surface areas which result inloss of valuable liquid product and excessive gaseous product,-excessive residue, excessive heating of the catalyst during burning,loss of valuable heat values, higher oxygen demands, and otherdisadvantages.

In addition, a large amount of fine (e.g. minus 14 U .5. Standard Sievesize) particulate spent shale is usually present during burning andreheating. This spent shale contains organic carbon and increases oxygendemands, causes loss of useful heat values, and adversely enlarges thesize of equipment. Fine spent shale or other materials also interferewith control of the burning and other stages of the process and createmany other problems especially when the entrained spent shale is smallerthan other heat-carrying bodies. Moreover, the presence of appreciableamounts of fine spent shale severely limits the type of equipment whichcan be used for burning the residue. Generally, burning in the presenceof fine spent shale requires the use of lift pipes. If air is used forlifting, the burning could entail a large excess of oxygen which wouldrapidly burn the organic matter and create disadvantages in the processof this invention.

Copending application Ser. No. 410,200, which is a continuation-in-partof application 284,288, and which is incorporated herein, provides aprocess for retorting oil shale using hot special pellets as a retortingmedia in a way which regulates the amount of combustible organic carbonresidue or deposition formed on the pellets during retorting of oilshale and improves the recovery of useful components and liquid productdistribution. The deposition acts as a principal source of fuel forheating the pellets, and the sensible heat in the pellets is used toretort the oil shale. The process relies on the interrelation betweenthe surface area of the pellets and other conditions and variables;however, additional flexibility in the operation of the process,especially the retort zone, is desired primarily because it has beenfound that the retorting stage of the process requires constant controland adjustment. There also arises occasions when the objectives orconditions of the retorting process change or fluctuate and more processflexibility is advantageous. For example, the richness of the raw oilshale will vary with time, or it may be desirable to use higher internalsurface area pellets and to make allowance for surface area changes asthe pellets are cycled. At other times, a change in heat capacity of theretorting media may be desirable. Briefly, therefore, a principal objectof this invention is to provide greater flexibility to a retortingprocess of the type disclosed in copending application Ser. No. 410,200filed Oct. 26, 1973.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, FIG. 1 is a schematicflowsheet of the process of this invention; and

FIG. 2 is a partly schematical, partly diagrammatical flow illustrationof a system for carrying out a preferred sequence of the process of FIG.1.

SUMMARY OF THE INVENTION In a retorting process, crushed carbonaceoussolid organic matter is retorted in a retort zone with hot special heatcarriers in a manner which produces product gases and oil vapors,combustible deposition, and particulate spent shale. The primaryobjectives of the process are to improve product quality and the productyield of an overall commercial oil shale process, to reduce the need forgaseous or liquid fuels which are normally required in the production ofsyncmde from solid carbonaceous materials, and to avoid waste ofvaluable organic residue. The process cycles special heat carriers in asize range between about 0.055 inch and 0.5 inch and preferably between0.055 and 0.375 inch, and comprised of a mixture of low internal surfacearea heat bodies and relatively high internal surface area pellets. Theheat carriers contain between and 90 percent by weight of the heatbodies and between 90 and 10 percent by weight of the pellets. Thephysical properties and characteristics, especially surface area, size,shape, temperature, and amount, of the heat carriers coact with othervariables to produce a regulated amount of a combustiblecarbon-containing deposition on the pellets. This renders the depositionon the pellets more useful as a fuel for heating the heat carriers. Inthe process, some or all of this deposition on the pellets is burned ina pellet combustible deposition burning zone after the heat carriershave been separated from the spent shale to heat and reheat the heatcarriers. The pellets have a surface area at least as great as squaremeters per gram of pellets. The low surface area heat bodies have asurface area less than 0.1 square meters per gram, and increase the heatcapacity or sensible heat of the heat carriers and coact with thepellets to regulate the effective surface area and quantity of the heatcarriers relative to the oil shale. The low surface area heat bodies,therefore, provide greater flexibility to the retorting process. Thecombined average surface area of the heat bodies and pellets in the heatcarriers is between 10 and 150 square meters per gram.

In the process, mined oil shale which contains solid carbonaceousorganic matter and other mineral matter and which has been crushed andmay have been preheated is pyrolyzed or retorted in a retort zone withthe hot special heat carriers at a temperature and in an amountsufiicient to provide at least 50 percent of the sensible heat requiredto retort the oil shale. Retorting the shale produces gas and oilproducts which are recovered and particulate spent shale. Retorting alsotends to deposit the combustible carbon-containing deposition on thepellet portion of the heat carriers. Preferably, the amount ofcombustible deposition formed on the pellet portion upon passage throughthe retort Zone is on an average less than 1.5 percent by weight of theheat carriers.

After retorting the oil shale, preferably, at least 75 percent of thetotal particulate spent shale and at least percent of the particulatespent shale smaller than the heat carriers are separated from the heatcarriers. This separation is performed before the buning of thecombustible deposition on the pellets. Preburn separation avoids theproblems caused by the presence of fine matter during burning. One wayto accomplish this sparation is to first screen large spent shale andagglomerates from the heat carriers and thereafter subject the heatcarriers and spent shale to gas elutriation with a noncombustionsupporting gas. A way to enhance the degree of total separation is tocontrol the spericity factor of the heat car riers to at least 0.9, orto crush the raw oil shale to a smaller than normal size, that is, tominus 6 US. Sieve Series size.

After separation of the spent shale, the heat carriers are passed to apellet deposition burning zone where at least a portion of thedeposition on the pellets is burned to reheat the heat carriers.

DETAILED DESCRIPTION OF THE INVENTION The process for retorting ofcrushed oil shale containing carbonaceous organic matter and othermineral matter is described in general terms having reference to FIG. 1and in more particular terms by reference to FIG. 2.

Raw or fresh oil shale which has been mined and pulverized, crushed orground for the most part to a predetermined maximum size for handling ina retorting system by any suitable particle diminution process is feddirectly from a crusher or from a hopper or accumulator by Way of shaleinlet line 11 into rotating retort zone 13. At the same time, a specialmixture of heat carriers comprised of high surface area pellets and lowsurface area bodies substantially hotter than the shale feed are fed bygravity or other mechanical means to the retort zone by way of retortinlet pipe 15. The heat carriers and shale feedstock could be fed to theretort zone by way of a comon retort zone inlet.

For purposes of this invention, any spent shale or residual oil shalematerial cycled with the heat carriers is not considered as being a partof the heat carriers.

Crushing of the raw mined shale expedites more uniform contact and heattransfer between the shale feedstock and hot heat carriers. In normalpractice, the degree of crushing is simply dictated by an economicbalance between the cost of crushing and the advantages to be gained bycrushing when retorting the kerogen from the shale. Generally the shalefeedstock is crushed to about out-half inch and no particular care istaken to produce or restrict production of finer material. In thisprocess, crushing has a special purpose and aids in a pre- -burnseparation step. In one embodiment for reasons which will be hereinaftershown and despite the added costs and standard practice, the mined shaleis crushed to a substantially finer size wherein at least 95 percent byweight of the crushed oil shale Will pass through a U.S. Sieve Seriessize 6 screen.

The crushed oil shale may or may not be. preheatedi by direct orindirect heat from any source including. in-

direct heat exchange with heat carriers or flue gases generated duringthis retorting process. If the shale feedstock is preheated, thetemperature of the feedstock will not exceed 600 F. The shale feedstockwill usually be fed by way of a metered weight controller system forreasons hereinafter made apparent and which may include a preheat and/or gas lift system. The preferred system for preheating the raw shale isto lift the shale in lift pipes with the hot flue gases generated in thecombustion phase of the process.

The hot special heat carriers are comprised of a mixture of particulateheat bodies and pellets. The mixture contains at least between and 90percent by weight of heat bodies and between 90 and 10 percent by weightof pellets and are especially characterized by having a size during useof between approximately about 0.055 inch and 0.5 inch and preferablybetween 0.055 inch and 0.375 inch, and a combined average surface areaof the pellets and bodies in the heat carriers during use of between 10and 150 square meters per gram. The surface area is the averageeffective surface area upon entry into the retort zone. The surface areamay be determined by the conventional nitrogen absorption method. In oneembodiment of the process of this invention, the surface area of theheat carriers on a gram basis is between 10 and 100 square meters. Theimportance of surface area is hereinafter discussed in detail. The heatcarriers are at a temperature ranging between 1000 F. and 1400 F. whichis about 100 F. to 500 F. higher than the designed retort temperaturewithin the retort zone. The most favorable practical temperature rangedepends on the process variables and more particularly on the specificadvantages and characteristics of this process. The quantity of heatcarriers is controlled to coact with other variables so thatcarrier-to-shale feedstock ratio on a weight basis is preferably betweenone and three with a ratio betwen 1.5 and 2.5 being more preferred. Thisratio is, moreover, such that that sensible heat in the heat carriers issuflicicnt to provide at least 50 percent of the heat required to heatthe shale feedstock from its feed temperature to the designed retorttemperature. The feedstock feed tempera ture is the temperature of theoil shale after preheating, that is, the temperature of the shale uponentry into the retorting zone. The average retort temperature rangesbetween about 850 F. and 1200" F. depending on the nature of the shalefeedstock, the heat carrier-to-shale ratio, the type of productdistribution desired, and heat losses. The relative mass and size of theheat carriers are selected in a manner hereinafter set forth whichfacilitates separation of the heat carriers from spent shale, controlsthe amount of combustible residue deposited on the pellet portion of theheat carriers, optimizes other facets of the retorting process, andmakes allowance for wear or size reduction of these pellets as they arecycled and recycled through the retorting process.

Heat carriers are subdivided or particulate solids. A majority of thesesolids have the characteristics and properties herein required and arecomposed of the same or dissimilar materials having sufficient strengthand of irregular shape, cylindrical shape, approximately oval orspherical shape, or purely spherical shape. The preferred heat carriershave a sphericity factor of at least 0.9 which, in addition to the usualadvantages of facilitating movement of the heat carriers through theretorting process and of providing optimum solid-to-solid heat transferand contact between the heat carriers and oil shale feedstock, has anadvantage particularly useful in separating the heat carriers from othersolids produced in the process as hereinafter set forth. The sphericityfactor is the external or geometric surface area of a sphere having thesame volume as the heat carrier particle divided by the external surfacearea of the heat carrier particle.

The pellets in the pellet portion of the heat carriers are made up ofmaterials, such as, alumina or silica alumina, which are not consumed inthe process and which are subdivided or particulate matter havingsignificantly high internal surface area. The low surface area bodies ofthe heat carriers are made up of materials other than spent shale, .suchas, quartz, beads, silicon carbide, zirconia, sand, and the like, whichare not consumed in the process and which are subdivided or particulatematter having no practical or significant internal surface area. Theheat carriers are sufliciently wear or breakage resistant and heatresistant to maintain their physical characteristics under theconditions employed in the process, to effect retorting of the oilshale, and to permit controlled burning of a carbon-containingdeposition formed on the pellets during such retorting. Morespecifically, the heat carriers do not disintegrate or decompose, meltor fuse. The pellets, moreover, do not undergo excessive surface areareduction at the temperatures encountered during such burning and thethermal stresses inherent in the process. The heat carriers will, ofcourse, undergo some gradual wear or size reduction.

As will be shown, the size of the heat carriers is related to the othervariables and to the preburn separation step to the other variables andto the preburn separation step in a size range between about 0.1 inchand 0.5 inch and preferably between 0.1 inch and 0.375 inch, and willfor the most part be maintained during use at a plus 14 US. Sieve SeriesScreen size, that is, approximately about 0.055 inch or greater. Finerheat carrier grain sizes are undesirable in the process of thisinvention.

The retort zone is any sort of retort system which causes intimatecontact or mixing of the crushed oil shale and heat carriers. Thepreferred retort is any sort of horizontal or inclined retorting drumthat causes the oil shale and heat carriers to undergo a tumblingaction. This sort of retort is herein referred to as a rotating retortzone. This type of retort zone is quite flexible over a wide range ofconditions and more specifically has the advantages of causing rapidsolid-to-solid heat exchange between the heat carriers and shalefeedstock thereby flashing and pyrolyzing the oil and gas vapors fromthe shale in a way which allows the vapors to separate from the solidswithout passing up through a long bed of solids and which minimizesdilution of the product vapors by extraneous undesirable retortinggases; of allowing for a high shale throughput rate at high yields for agiven retort volume; of providing for greater control over residencetime; of aiding in preventing overcoking and agglomeration of the heatcarriers and shale; of facilitating formation of a more uniformcontrolled amount of combustible carboncontaining residue on the surfacearea of the pellets in the heat carriers; and of causing flow of theheat carriers and shale through the retort zone in a manner which aidsin eventual separation of the heat carriers from the spent shale. Theamount of deposition deposited on the pellets in the heat carriers is animportant feature of this process and will be discussed later in moredetail. The retorting process is carried out in concurrent or parallelflow fashion with the hot heat carriers and the raw shale feedstockbeing fed into the same end of the retort. The retort zone may bemaintained under any pressure which does not hamper efficient operationof the retort, interfere with production of valuable retort vapors, orcause excessive deposition of residue on the pellets in the heatcarriers. Generally, pressurization of the pyrolysis or retort zonecauses considerable difficulties especially if a rotating retort zone isused. The pressure employed is, therefore, generally the autogenouspressure.

In the retort zone, the hotter heat carriers and cooler crushed shalefeedstock are admixed and intimately contacted almost immediately uponbeing charged into retort zone 13. The shale particles are rapidlyheated by sensible heat transfer from the heat carriers to the shale.Any water in the shale is distilled and the kerogen or carbonaceousmatter in the shale is decomposed, distilled, and cracked into gaseousand condensable oil fractions, thereby forming valuable vaporousefiluents including gas, oil

vapors, and superheated steam. Pyrolysis and vaporization of thecarbonaceous matter in the oil shale leaves a particulate spent shale inthe form of the spent mineral matrix matter of the oil shale andrelatively small amounts of unvaporized or coked organiccarbon-containing material. This retorting process more than 100 percentof Fischer Assay if the total usable products are added, that is, thegas, the oil, and deposition on the pellets in the heat carriers.

As the aforementioned vaporous effluents are formed, a combustiblecarbon-containing deposition or residue is formed or deposited on thecontrolled surface area of the pellets in the heat carriers. It has beenfound that the variables involved in this process as herein set forthmay be related in a manner which aids in regulation of the amount ofcarbon-containing deposition thus deposited and at the same time makeallowance for the fact that the original kerogen content of the rawshale feedstock and some other process conditions will intrinsically andperiodically vary. The amount of deposition formed or deposited on thepellet portion of the heat carriers upon passage through the retort zoneis suflicient upon combustion to provide at least 50 percent of the heatrequired to reheat the heat carriers and is preferably on an averageless than 1.5 percent by weight of the heat carriers per pass throughthe retorting zone. The more preferred deposition range is between 0.8and 1.5 percent. Basically, the amount of deposition on the heatcarriers is important since as will hereinafter be shown this depositionis burned in a controlled manner to generate a major portion of the heatnecessary for heating the heat carriers to carry out the retorting phaseof the process. In addition to decreasing efliciency, excessivedeposition increases greatly the possibility of overheating the pelletsin the heat carriers and destroying or excessively altering theirinternal surface area. The total amount of deposition also affects theultimate relative yields of gas and condensable or final liquefiedproducts. This in turn affects the distribution of various boiling pointfractions in the liquefied products. The amount of deposition depositedis basically controlled in this process by the interrelation of severalvariables, such as, heat carrier-to-shale ratio, the size and inlettemperature of the heat carriers, the retort temperature, the surfacearea of the pellets and of the entire heat carrier mixture. The surfacearea of the mixture is regulated by the proportion of low surface areabodies to the pellets and by the surface area of the pellets. Additionalcontrol over both the total amount of deposition deposited on thepellets may be obtained by residence time or throughput rate, partial orcomplete combustion of the deposition, controlled residue combustiontime or amount of oxidizing gas used during burning, the catalyticcharacteristic of the pellets, and the size of the pores at the surfaceof the pellets. As can be readily seen by this description of theprocess, the degree of control provided by a single variable is neverindependent and the flexibility of control varies with the type ofvariable.

The average surface area of the combined heat bodies and pellets in theheat carriers is considered one of the most important variables. Thetest results of Tables 1, 2, and 3, which were obtained on pelletsalone, illustrate the effect of surface area. The effect of pelletsurface area on the amount of carbon-containing deposition formed on thepellets and on the distribution of carbon deposition between the pelletsand spent shale is illustrated in Table 1. Table 2 illustrates theeffect of pellet surface area on liquid product distribution when amodified Fischer retort was used. The effect of pellet-to-shale ratioand, therefore, total surface area of the pellets is illustrated inTable 3. The results illustrated in these tables lead to severalconclusions. If the surface area is less than ten square meters pergram, either too little total deposition will be formed or the burningof the deposition will not be sufficient to provide a major portion ofthe heat required to heat the heat carriers to the desired temperatureand to carry out the retorting phase of this process. This wouldnecessitate the use of supplementary fuels and as indicated previously,this has significant disadvantages to the objects of this process. Ifthe average surface are-a of the heat carriers exceeds 150 square metersper gram, too much total deposition will be formed.

In this invention the surface area of the heat carriers is regulated byblending the low surface area heat bodies with the high surface areapellets. The surface area of the heat bodies is far less than 0.1 squaremeters per gram of heat bodies and is for all practical purposesnegligible. The proportion of pellets to low surface area heat bodiesprovides adjustment to the heat carrying capacity of the mixture tosupply sufficient sensible heat to carry out the retorting phase of theprocess. Consequently, the mixture of heat bodies and pellets mustcontain at least 10 percent and less than percent by weight of heatbodies to meet the requirements and functions of this invention. Themixture must also contain at least 10 percent and less than 90 percentby weight of pellets. By Way of example, the total surface area of thepellets is determined by the surface area per gram of pellets and thetotal grams of pellets used. The total grams of pellets are controlledby the heat carrier-to-oil shale feedstock ratio, the fraction of theheat carriers that are pellets, and the shale throughput rate. If thepellets in the heat carriers have an average surface area of 200 squaremeters per gram, a fifty-fifty mixture of pellets and low surface areaheat bodies will have an effective surface area of about 100 squaremeters per gram.

TABLE 1.EFFECT OF PELLET SUR- FACE AREA ON CARBON DEPO- SI'IION Wt.percentage of carbon on- Residual Pellets shale U. 725 3. 90 0. 89 3. 650. 93 3. 95 0. 9a 3. 71 46 1. 24 3. 49 No pellets 4. 30

TABLE 2.EFFEOT OF PELLET SURFACE AREA ON LIQUID PRODUCT DISTRIBU- TIONPellet area Product No boiling range pellets 47 mJ/g. 96 mfl/g.

150400 F 12% 27 a 34% 400700 F 37% 46% 48% 700-900 F 32% 22% 14% 900 F.+19% 5% 4% *PelletzShale ratio=2:1

As illustrated in Tables 2 and 3, the surface area of the pellets and,therefore, the surface area of the heat carries affect liquid productdistribution. Increasing the surface area of heat carriers tends todecrease the yield of condensable product vapors and increase productionof gases. As a result, all variables being considered, it has been foundthat heat carrier surface areas between 10 and 150 square meters pergram are acceptable with surface areas between 10 and square meters pergram being preferred and that heat carrier-to-shale ratios between oneto three are preferred with ratios between 1.5 and 2.5 being morepreferred.

As illustrated in Table l, of particular additional significance is thefact that a substantial portion of the combustible deposition on thepellets comes from the residual carbonaceous material that wouldnormally be left on the spent shale. In other words, the organic carbonmaterial that is normally left on the spent shale divides itself betweenthe pellets and the spent shale. This process, thereby, recovers residuethat would normally be lost with the spent shale. The recovered residueis then made useful as fuel for heating the pellets. At first glance,this recovery may seem small, but when it is remembered that the organiccontent of the oil shale is small, it can be seen that this increasedrecovery and utility of the residue is quite significant.

The mixture of heat carriers and shale moves toward retort exit 17 andthe gaseous and vaporous effluents containing the desired hydrocarbonvalues separate from the mixture. Since there is no need to use carrier,fluidizing, or retorting gases in the retort zone, the vaporous efiluentis able to leave the retort essentially undiluted by extraneous fluidsexcept for any water or steam vapor added to prevent or retardcarbonization, or to sweep product vapors from the solids, or for otherreasons to the retort or the efiluent collection chamber. In a rotatingretort system, the mixture movement is continuous and is aided by theaction or design of this type of retort and by continuous withdrawing ofheat carriers and spent shale from the exit end of the retort zone. If arotating retort zone is used, caking or coking together of the heatcarriers or spent shale will be kept low. Moreover, a rotating type ofretort zone is especially suited to varying the residence time, that is,the length of time that the shale and heat carriers remain in the retortzone by allowing variations in heat carrier-to-shale ratio and volume ofshale throughput. As previously indicated, greater than normal leeway incontrol over these variables is especially advantageous to regulation ofthe amount of deposition deposited on the pellets during the retortstage of the process. The residence time required is on the order ofabout three to about twenty minutes with residence times of less thantwelve minutes for the heat carriers being preferred. The shaleresidence time depends on its flow or movement characteristics and sincethe shale is not uniform in size and shape, the shale residence timevaries.

The mixture of heat carriers and spent shale exits from retort zone 13at a temperature between 800 F. and 1150 F. by way of retort exit 17into separation zone 19 for separation of the vapor, heat carriers, andspent shale. The separation zone may be any sort of exiting andseparation system accomplishing the functions hereinafter mentioned andmay be comprised of any number of units of equipment for separating andrecovering one or more of these three classes of retort zone efiluentseither simultaneously, or in combination, or individually. In theprocess of this invention, it is highly desirable that at least 75percent of the total spent shale be separated from the heat carriers inthe separation zone to eventually be collected in separation zone exitline 21. In addition, at least 95 percent of the spent shale smallerthan the heat carriers, that is, smaller than about 0.055 inch, areseparated. As shown in FIG. 2, the retort zone mixture is first passedthrough revolving screen or trommel 23 which has openings or aperturessized to pass the heat carriers and spent shale of about the same orsmaller size than the heat carriers. The trommel extends into productrecovery chamber 25. In the trommel, the gaseous and vaporous productsseparate from the mixture of heat carriers and spent shale and, at thesame time, large spent shale particles or agglomerates are separatedfrom the heat carriers and spent shale. Spent shale and heat carriersflow through the openings in trommel 23 and drop to the bottom ofrecovery chamber 25 to exit via retort exit line 27. Any rocks or spentshale too large to pass through the openings in the trommel pass outwardthrough exit 29. The product vapors and gases resulting from retortingthe oil shale collect overhead in recovery chamber 25 and rapidly passto overhead retort products line 31 at an exit temperature between about750 F. and 1050 P. where the product vapors are subjected either intheir vaporous or condensed state to hot dust separation (not shown) andpassed to other stages (not shown) of the overall operation. The hotdust separation may be interior or exterior, or both, of recoverychamber 25 and the dust thus collected may be combined and handled withother spent shale. Hot dust or fines separation may be accomplished byhot gas cyclones, quenching and washing, agglomeration with sludge or aseparately condensed heavy product fraction, centrifuging, filtration,or the like.

As mentioned previously, the gases produced in the retort zone need notbe diluted by extraneous retort gases and are, therefore, readily usedin the overall shale opera tion. Some gas may be needed forsupplementary fuel and some for production in the usual manner ofhydrogen if hydrogenation is used in the overall shale operation. Theoptimum amount of gas production is enough to satisfy these requirementsas this process stresses liquid oil products.

As shown in FIG. 2, the spent shale and heat carriers in recoverychamber 25 are discharged via exit line 27 at a temperature betweenabout 750 F. and 1050 F. where these particulate solids are passed orconducted by gravity or other means of conveyance to gas elutriationsystem 33 which is a part of separation zone 19. In the elutriationsystem, a major portion, and more preferably substantially all, of theremaining spent shale is separated from the heat carriers. It isessential that elutriation be accomplished in a way which retains thedesired amount of combustible deposition deposited on the pellet portionof the heat carriers; consequently, the elutriating gas fed by line-35is a noncombustion supporting gas. By conducting the process with heatcarriers in the size range between about 0.055 inch and 0.5 inch, andpreferably between 0.1 and 0.375 inch, at least 75 percent of the totalspent shale may be separated by action of the trommel and subsequent gaselutriation at a velocity of between 18 and 2.5 feet per second if mostof the raw shale feedstock was crushed to minus three-fourths inch.Based on an average of six sieve analyses of the spent shale produced byretorting half-inch shale feedstock in a rotating retort using ceramicone-half inch balls, about 16 percent by weight (analyses range 8% to27%) of the spent shale is retained on a U.S. Sieve Series size 14screen which is in a size range similar to the heat carriers. Gaselutriation with irregular or cylindrical shaped heat carriers onlyseparates about 2.0 to 4.0 percent of this portion of the spent shalefrom the heat carriers. Therefore, on an average between 12 and 13percent of the spent shale is difiicult to separate by screening andelutriation depending on whether the heat carriers cover the entire sizerange of this part of the spent shale. As mentioned previously,retention of more than 25 percent of the spent shale interferes withproper operation of the pellet deposition burning zone even if most ofthe spent shale entering the burning zone is originally in the same sizerange as the heat carriers. Upon combustion, this spent shale woulddistintegrate further to fine ash and cause erratic operation of thecombustion zone and other operating difficulties. In addition, someallowance is made for spent shale and ash buildup as the heat carriersare cycled and recycled through the process.

Since the spent shale having a size similar to the heat carriers isdifficult to elutriate while the spent shale smaller than the heatcarriers is readily separated by elutriation, and practically complete,it is desirable to alter the characteristics of the spent shale or ofthe heat carriers to accomplish a greater degree of separation whileholding heat losses in the heat carriers to a reasonable level. One wayto accomplish this objective is to crush at least percent by weight ofthe shale feedstock to a minus 6 screen size. This results in aseparation of at least 95 percent by weight of the total spent shalefrom the heat carriers and the trommel may also be eliminated. Asmentioned previously, crushing to this size is costly and normally notdone; however, in view of the fact that in this invention it isessential that the bulk of the spent shale be separated from the heatcarriers prior to reheating of the heat carriers, the cost of additionalcrushing may be justified. Another way to accomplish the objective ofthis separation prior to reheating the heat carriers has beendiscovered. It has been found that if the heat carriers are essentiallyspherical, that is, have a sphericity factor of at least 0.9, theefiiciency of separation by gas elutriation is greatly increased even ifthe raw shale is not crushed to a finer size. Spherical heat carriershave improved flow properties over the spent shale and for a givenscreen size particle exhibit greater weight per particle. Gaselutriation with spherical heat carriers will separate about 97 percentor more of the total spent shale retained on a U.S. Sieve Series size 14screen and will provide almost complete separation of the smaller spentshale. Thus, if spherical heat carriers are used, gas elutriation willseparate at least 95 percent of the total spent shale. As mentionedpreviously, therefore, the preferred shape of the heat carriers isspherical, that is, the preferred heat carriers have a sphericity factorof at least 0.9.

The separated spent shale is carried out of the elutriating chamberoverhead through line 37 to dust cyclone 39 where the spent shale iscollected and may be combined and handled with other spent shale foreventual compaction and waste disposal or sale for use in manufacturingother products.

The separated heat carriers with a combustible deposition deposited onthe pellet portion thereof are then passed from the separation zone to apellet deposition burning zone via heat carrier return line 41 tolifting system 43 Where the heat carriers are lifted preferably to anelevation which allows gravity feed to retort zone 13 by way of liftline 45 to pellet deposition burning zone 47, which as shown in FIG. 2has surge hopper 49 for collecting the lifted heat carriers and levelingout fluctuations and from which the heat carriers fall into combustionzone 51. While any conveying and lifting system holding heat losses to areasonable value may be used, it is preferred as shown in FIG. 2 thatthe lifting system be a pneumatic conveying system which will operate inthe conventional manner to lift the heat carriers to the pelletdeposition burning zone. The lift gas enters the lift system via line 53at a velocity between 25 and 70 feet per second and the lift time is,therefore, very short. As a result, air may be used as the lift gaswithout causing uncontrolled and appreciable combustion of thedeposition on the pellet portion of the heat carriers and thedetrimental effects attendant to such uncontrolled burning.

As mentioned previously, the pellet portion of the heat carriers bears acombustible carbon-containing deposition which was absorbed or depositedduring retorting of the oil shale. This combustible deposition is burnedin combustible pellet deposition burning zone 47 to provide at least 50percent or more of the heat required to reheat the heat carriers to thetemperature required to effect retorting of the shale. The combustibledeposition is burned in a manner similar to the way that catalyticcracking catalysts particles are regenerated and which would excessivelyreduce the combined effective surface area of the heat carriers to lessthan ten square meters per gram. A progressive bed burner with a gasflow of about one to two feet per second is preferred. A comhustionsupporting gas, for example air, a mixture of air and fuel gas generatedin the process, flue gas with the desired amount of free oxygen, isblown into the pellet deposition burning zone at a temperature at whichthe deposition on the pellets in the heat carriers is ignited by way ofcombustion gas inlet 55 which in FIG. 2 includes a blower. Steam mayalso be used to control burning provided that the steam does notexcessively reduce the surface area of the pellets in the heat carriers.The combustion supporting gas may be preheated in heaters 57 by burningsome of the gases produced in the process to reheat the heat carriers tothe minimum ignition temperature. The quantity of combustion supportinggas, e.g. about ten to fifteen pounds of air per pound of deposition,affects the total amount of deposition burned and the heat generated bysuch burning and in turn the temperature of the heat carriers. The bulkdensity and specific heat of the heat carriers will vary and will, ofcourse, depend on the materials used to form the heat carrier mixture.The gross heating value of the carboncontaining deposition is estimatedto be about 15,000 to 18,000 Btu. per pound. The amounts of carbondioxide and carbon monoxide produced in the flue gases created byburning the deposition indicate amount of combustion supporting gasrequired or used and the amount of carbon-containing deposition notburned. Generally, it is desirable to attempt to burn all of thedeposition on the pellets. In any case, as a general rule, at leastfifty percent of the deposition is burned.

The unburned deposition is returned to the retort zone with the heatcarriers. In this manner, the total amount of carbon-containingdeposition deposited per cycle on the heat carriers is also regulated tosome degree. It should be noted that this type of controlled burningdoes not selectively burn the same amount of deposition from everypellet. Other factors taken into consideration during burning of thisdeposition are the heat carrier porosity, density, and size, the burnerchamber size and heat carrier bed size, residence burning time, thedesired temperature for the heat carriers, heat losses and inputs, theheat carrier and oil shale feed rates to the retort zone, and the like.The residence burning time Will usually be rather long and up to aboutthirty to forty minutes. Combustion of the deposition should becontrolled in a manner which does not heat the heat carriers to above1400" F. The hot flue gases generated in the pellet deposition burningzone may be removed by burning zone exit line 59 and used to preheatcool raw shale feedstock or for heat transfer to any other phase or partof the shale operation. For example, this stream could be fed to acarbon monoxide boiler and the heat available from the boiler could beused for processing product vapors or to drive turbines. Of course,additional fuel material or gases may be used to supplement burning ofthe combustible pellet deposition if this is necessary, but it is to beunderstood that burn ing of the deposition on the pellet portionsupplies the major portion of the sensible heat required for retortingof the shale and that the variables are set to accomplish this objectivealong with the other advantages and objectives of this process.

-A continuous stream of hot heat carriers having a temperature between1000 F. and 1400 F. is thereby produced for return and introduction backthrough heat carrier inlet pipe 15 into retort zone 13. As previouslyindicated, the rate of return of the heat carriers will be metered orcontrolled in conventional manners to correspond to the crushed raw oilshale feed rate, the organic content of the raw oil shale, the optimumheat carrierto-oil shale feedstock ratio, the desired distribution ofproducts, and to the other variables previously described.

Although the retorting process is carried out in a manner to hold lossof pellets and other heat carriers to a minimum, some will be lost inthe process and a relatively small quantity of pellets or other heatcarriers may be added continuously to maintain the desired quantity ofheat carriers.

The foregoing description of the conditions and variables of the processillustrates a preferred method of conducting a retorting process.Reasonable variations and modifications are practical within the scopeof this disclosure without departing from the spirit and scope of theclaims of this invention. For example, while the disclosure of thisprocess and the variables have been limited to oil shale, the processconcepts lend themselves readily to retorting of any solid organiccarbonaceous material containing hydrocarbon values which can berecovered by thermal vaporization of the solid carbonaceous material,such as, for example, coal, peat, and tar sands. By way of furtherexample, while only a single train of units and stages have beendescribed, it is to be understood that any stage or zone could becomprised of more than one stage or zone, each of which could beoperated under different conditions to provide the overall combinedeffect set forth.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. In a method for retorting crushed oil shale containing carbonaceousorganic matter and mineral matter wherein oil shale is retorted bycontacting said oil shale with particulate hot heat carriers in a retortzone to gas and oil products, particulate spent shale, and an organiccombustible deposition on at least a portion of said heat carriers, saidheat carriers having been heated in a deposition burning zone to aretort zone inlet temperature of between 1000 F. and 1400 F. mainly bycombustion of a combustible carbon-containing deposition on said heatcarriers, said heat carriers being in an amount sufficient to provide atleast 50 percent of the heat required to vaporize a major portion of thecarbonaceous matter from said oil shale and to heat said crushed oilshale from its retort zone inlet temperature to a retort zone outlettemperature of between 800 F. and 1150 F., and wherein said gas and oilproducs are separated and recovered, the improvement wherein said heatcarriers are comprised of particulate heat bodies and pellets in a sizerange between about 0.055 inch and 0.5 inch, said heat bodies having alow surface area less than 0.1 square meter per gram of said heatbodies, said pellets having a relatively high surface area at least asgreat as 20 square meters per gram of said pellets, said heat carrierscontaining between 10 and 90 percent by weight of said heat bodies andbetween 90 and 10 percent by weight of said pellets, and the combinedaverage surface area of said heat bodies and said pellets in said heatcarriers being between 10 and 150 square meters per gram.

2. The method according to claim 1 wherein the pellets are in a sizerange between about 0.055 inch and 0.375 inch.

3. The method according to claim 1 wherein at least 75 percent by weightof the total of said spent shale and at least 95 percent by weight ofthe portion of said spent shale that is smaller in size than said heatcarriers is separated in a separation zone from said heat carriers afterretorting of said oil shale but prior to said heating of said heatcarriers by combustion of said deposition on said heat carriers.

4. The method according to claim 1 wherein the amount of said heatcarriers is such that the ratio of said heat carriers to said crushedoil shale in said retort zone on a weight basis is between one andthree.

5. The method according to claim 4 wherein at least 75 percent by weightof the total of said spent shale and at least 95 percent by weight ofthe portion of said spent shale that is smaller in size than said heatcarriers is separated in a separation zone from said heat carriers afterretorting of said oil shale but prior to said heating of said heatcarriers by combustion of said deposition on said heat carriers.

6. A method for retorting of crushed oil shale containing carbonaceousorganic matter and mineral matter comprising:

(a) feeding crushed oil shale and heat carriers to a retort zone, saidheat carriers being comprised chiefly of particulate heat bodies andpellets in a size range between about 0.055 inch and 0.5 inch, said heatbodies having a low surface area less than 0.1 square meter per gram ofsaid heat bodies, said pellets having a relatively high surface area atleast as great as 20 square meters per gram of said pellets, said heatcarriers containing between 10 and percent by weight of said heat bodiesand between 90 and 10 percent by weight of said pellets, the combinedaverage surface area of said heat bodies and said pellets in said heatcarriers being between 10 and 150 square meters per gram, said heatcarriers being at a retort zone inlet temperature between 1000 F. and1400" F. and in a quantity such that the ratio of said heat carriers tosaid crushed oil shale entering said retort zone on a weight basis isbetween one and three, said ratio also being such that the sensible heatin said heat carriers is sufficient to provide at least 50 percent ofthe heat required to heat said crushed oil shale from its retort zonefeed temperature to a retort zone outlet temperature of between 800 -F.and 1150 F.;

(b) retorting in said retort zone gas and oil products from said crushedoil shale, thereby forming particulate spent shale and a combustibledeposition on said pellets in said heat carriers;

(0) causing said heat carriers and said spent shale to pass from saidretort zone to a particle separation zone and separating from said heatcarriers at least 75 percent by weight of the total spent shale and atleast percent by weight of the portion of said spent shale that issmaller in size than said heat carriers prior to heating said heatcarriers in a combustible deposition burning zone;

((1) recovering gas and oil products generated by retorting of saidcrushed oil shale;

(e) passing said heat carriers from said separation zone to saidcombustible deposition burning zone;

(f) heating said heat carriers passed to said combustible depositionburning zone to an outlet temperature of between 1000 F. and 1400 F. byburning the combustible carbon-containing deposition on said pelletswith a combustion supporting gas; and

(g) thereafter passing said heated heat carriers from said combustibledeposition burning zone to said retort zone.

7. The method according to claim 6 wherein the pellets are in a sizerange between about 0.055 inch and 0.375 inch.

8. The method according to claim 6 wherein the average amount of saidcombustible carbon-containing deposition formed on said pellets in saidheat carriers upon passage through said retort zone is on said averageless than 1.5 percent by weight of said heat carriers.

9. The method according to claim 8 wherein said heat carriers have asphericity factor of at least 0.9.

10. The method according to claim 6 wherein the separation of step (c)is comprised of first passing said heat carriers and said spent shalethrough apertures in a trommel to screen out at least a portion of thespent shale and any agglomerates larger than said heat carriers, andthereafter subjecting the remaining heat carriers and spent shale to gaselutriation with a noncombustion supporting gas to effect furtherseparation of the spent shale from the heat carriers.

11. The method according to claim 10 wherein the average amount of saidcombustible carbon-containing deposition formed on said pellets in saidheat carriers upon passage through said retort zone is on said averageless than 1.5 percent by weight of said heat carriers.

12. The method according to claim 6 wherein said heat carriers have asphericity factor of at least 0.9 and at least 95 percent by weight ofthe total spent shale is separated from said heat carriers in step (c).

13. The method according to claim 12 wherein the average amount of saidcombustible carbon-containing deposition formed on said pellets in saidheat carriers upon passage through said retort zone is on said a'verageless than 1.5 percent by weight of said heat carriers.

15 14. The method according to claim 6 wherein at least 95 percent byweight of the crushed oil shale of step (a) has been crushed to a sizeto pass through a US. Sieve Series size 6 screen and at least 95 percentby weight of the total spent shale is separated from said heat carriersbined average surface area of said heat bodies and said pellets in saidheat carriers is between 10 and 100 square meters per gram.

17. The method according to claim 16 wherein the pellets are in a sizerange between about 0.055 inch and 0.375 inch.

18. The method according to claim 16 wherein the average amount of saidcombustible carbon-containing deposition formed on said pellets in saidheat carriers upon passage through said retort zone is on said averageless than 1.5 percent by weight of said heat carriers.

19. The method according to claim 18 wherein said heat carriers have asphericity factor of at least 0.9.

20. The method according to claim 16 wherein the separation of step (c)is comprised of first passing said heat carriers and said spent shalethrough apertures in a trommel to screen out at least a portion of thespent shale and any agglomerates larger than said heat carriers, andthereafter subjecting the remaining heat carriers and spent shale to gaselutriation with a noncombustion supporting gas to effect furtherseparation of the spent shale from the heat carriers.

21. The method according to claim 20 wherein the average amount of saidcombustible carbon-containing deposition formed onsaid pellets in saidheat'carriers upon passage through said retort zone is on said averageless than 1.5 percent by weight of said heat carriers.

22. The method according to claim 16 wherein said heat carriers have asphericity factor of at least 0.9' and at least percent by weight of thetotal spent shale is separated from said heat carriers in step (c).

23. The method according to claim 22 wherein the average amount of saidcombustible carbon-containing deposition formed on said pellets in saidheat carriers upon passage through said retort zone is on said averageless than 1.5 percent by weight of said heat carriers.

24. The method according to claim 16 wherein at least 95 percent byweight of the crushed oil shale of step (a) has been crushed to a sizeto pass through a US. Sieve Series size 6 screen and at least 95 percentby weight of the total spent shale is separated from said heat carriersin step (c).

25. The method according to claim 24 wherein the average amount of saidcombustible carbon-containing deposition formed on said pellets in saidheat carriers upon passage through said retort zone is on said averageless than 1.5 percent by weight of said heat carriers.

References Cited UNITED STATES PATENTS 3,008,894 11/ 1961 Culbertson208-11 3,018,243 1/1962 Nevens 208-11 3,020,227 2/ 1962 Nevens et al.20811 3,058,903 10/1962 Otis 20811 3,252,886 5/1966 Crawford 208113,573,197 3/1971 Gessner 20811 3,803,021 4/1974 Abdul-Rahman 208113,803,022 4/1974 Abdul-Rahman 20811 CURTIS R. DAVIS, Primary Examiner

1. IN A METHOD FOR RETORTING CRUSHED OIL SHALE CONTAINING CARBONACEOUSORGANIC MATTER AND MINERAL MATTER WHEREIN OIL SHALE IS RETORTED BYCONTACTING SAID OIL SHALE WITH PARTICULATE HOT HEAT CARRIERS IN A RETORTZONE TO GAS AND OIL PRODUCTS, PARTICULATE SPENT SHALE, AND AN ORGANICCOMBUSTIBLE DEPOSITION ON AT LEAST A PORTION OF SAID HEAT CARRIERS, SAIDHEAT CARRIERS HAVING BEEN HEATED IN A DEPOSITION BURNING ZONE TO ARETORT ZONE INLET TEMPERATURE OF BETWEEN 1000*F. AND 1400*F. MAINLY BYCOMBUSTION OF A COMBUSTIBLE CARBON-CONTAINING DEPOSITION ON SAID HEATCARRIERS, SAID HEAT CARRIERS BEING IN AN AMOUNT SUFFICIENT TO PROVIDE ATLEAST 50 PERCENT OF THE HEAT REQUIRED TO VAPORIZE A MAJOR PORTION OF THECARBONACEOUS MATTER FROM SAID OIL SHALE AND TO HEAT SAID CRUSHED OILSHALE FROM ITS RETORT ZONE INLET TEMPERATURE TO A RETORT ZONE OUTLETTEMPERATURE OF BETWEEN 800*F. AND 1150*F, ABD WHEREIN SAID GAS AND OILPRODUCTS ARE SEPARATED AND RECOVERED, THE IMPROVEMENT WHEREIN SAID HEATCARRIERS ARE COMPRISED OF PARTICULATES HEAT BODIES AND PELLETS IN A SIZERNGE BETWEEN ABOUT 0.005 INCH AND 0.05 INCH, SAID HEAT BODIES HAVING ALOW SURFACE AREA LESS THAN 0.1 SQUARE METER PER GRAM OF SAID HEATBODIES, SAID PELLETS HAVING A RELATIVELY HIGH SURFACE AREA AT LEAST ASGREAT AS 20 SQUARE METERS PER GRAM OF SAID PELLETS SAID HEAT CARRIERSCONTAINING BETWEEN 10 AND 90 PERCENT BY WEIGHT OF SAID HEAT BODIES ANDBETWEEN 90 AND 10 PERCENT BY WEIGHT OF SAID PELLETS, AND COMBINEDAVERAGE SURFACE AREA OF SAID HEAT BODIES AND SAID PELLETS IN SAID HEATCARRIERS BEING BETWEEN 10 AND 150 SQUARE METERS PER GRAM.